What is the "breaking capacity" of a switch?

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Phrazemaster

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So I found a candidate switch but I can't find what to me is a simple rating, the voltage rating. What it says in the datasheet is that the switch handles a "breaking capacity" of 250vac/250vdc (which sounds awfully high for this little guy)...I'm not sure that this is the same as the voltage rating of the switch? Or is it? I would hate to get it and find it some other kind of limitation on voltage that didn't appear in the datasheet...

Sigh...so much to learn.  :p

Thanks for any knowledgeable responses. I did a google first but it kept coming up with stuff about circuit breakers.

PS if you happen to know of a great little round illuminated switch for a phantom power circuit, by all means let me know!
 
Switches, fuses and circuit breakers all have this type of rating.  When a switch is opened, electricity tries to continue to flow by jumping the air gap.  The higher the voltage the bigger the air gap.  DC needs a even bigger air gap, because it doesn't drop to 0 Volts 100 or 120 times a second.  In general the higher the voltage rating, the more the switch contacts are optimized for this arcing.  For line level audio signals, chose switches with a lower voltage rating.
 
I agree, I think...seems like spec should read 'load breaking'  and have an amp rating, or watt rating. I work with 600 amp switches at my day gig; max 600 amps. We normally use 'load busters' to open these switches. Sometimes I have to open a damaged switch without a loadbuster and the arc 'drawn' is more dependent on load current than voltage: A switch feeding a transformer @ 7200 V will not really arc with no load on the secondary, but may continue to arc over once opened if loaded heavily.

so "breaking capacity" almost sounds like the point that the switch will 'fail'.
Is it made by a reputable manufacturer, or is it a bargain/knock-off, does it have a real data-sheet?

re: arcing/air gap, all true, contact material size and action also play into this equation.

round lit switch-- allied has nice ones as do mouser digikey newark rapid, etc.
need to do some searchin'
 
Hi, thanks for the thoughts...actually I've spent HOURS looking for the switch I have in mind, and may possibly have found it, thanks to your help. The problem is getting  a DPDT switch that's illuminated that also handles 48VDC...the reason for DPDT is I want the lamp to turn on/off when phantom power is applied, and I don't want to stick the lamp into the phantom circuit.

You would THINK it's kinda easy, but I've had quite a time finding what I wanted that also looked good for my project.

I would post a link to the farnell switch I have in mind, but the farnell links never work after I click them again later...sometimes the Mouser ones don't either. But Digikey always works!

So if you have any interest in going to Farnell.com and go to Farnell Exports, type in this part number: 0041-2372 and you'll see the switch and the datasheet.

So now that I found an expensive switch that might work, it might work TOO WELL and be too rugged for my poor little' ol' phantom power circuit?

Thanks again, I'll take the breaking capacity to mean the fail capacity and maybe give this switch a chance...unless you can see a reason why not.
 
farnell switch would work fine
nkk kb series from digikey are almost 1/4 cost.this was the first thing that came up probably many more out there that will suffice

with led illumination there is little current, and +48 for 1 mic is low current, I would use any switch for these functions, incandescent lamp would not worry me too much either, but led is safe bet--could even drive it from phantom supply.
 
Thank-you...I have seen those NKK switches...I can see them in my mind, without the Internet at this point...would you believe how many datasheets I have saved on my harddrive lol...so the NKK datasheets say they are good to 30VDC or 28VDC in some cases; are you saying this doesn't matter for phantom power? I know phantom power is not supposed to go over 10mA (according to an article I read recently), so because the amps are so low I can go beyond the rated values and work with 48v?

Thanks for your thoughts, very much.

Mike
 
I think you can look at it in terms of power: consider the function of volts and amps: inversely proportional for the same watts.
I could be wrong but still have had no trouble. As long as you are not switching considerable loads there should be no worry.
forum member burdij sells parts (white market) and has a few switches you could make work. But the usual domestic parts houses should have something that will cosmetically and electrically fit yer bill.
 
See, now this is exactly the kind of "down home" practical advice and thoughts I needed. Thank-you! I thought to myself, how silly, to think that a beautiful little switch that handles 5A @ 30VDC couldn't handle 10mA at 48VDC...I think I will take a chance.

"It's tough being a newbie, but somebody's gotta do it!"
 
Are you kiddin' me Shabtek? I just checked out burdij's stuff, and a store listed (Grove audio I think) and they have INCREDIBLE switches for a heck of deal...thank-you!! Wow I'm going to score some of those!
 
They're not exactly small but the Omron A16 (16mm) are excellent and available in DPDT alternate action with incandescent lamp or LED in 3 voltages and 5 colors. I use them to switch 24V but P48 would be no problem, even though they're rated for 30VDC like a lot of other small switches.

Cheers,

Michael
 
Thank-you for the tip Michael, much appreciated!

The world of illuminated phantom power switches broke open for me when shabtek said it's probably fine to use a switch rated lower, because I was going crazy trying to find a good looking switch that wouldn't break the bank with 48v specs...

I will check out that switch; thank-you sir! (it is sir, no?)

Mike
 
Yeah Michael I just checked out those switches; sweet! A bit pricey, maybe I can find them cheaper.

http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=Z1310-ND

Is a nice one...

Take care,

Mike
 
OK I finally pulled the trigger! (what? switches? yawn...)

Yah well for me I've been poring over datasheets forEVER man and I'm glad to finally have just gotten them ordered.

I do like the Omron ones, Michael, but I decided to go with some from Farnell. They are probably about the same price after delivery charges/euro conversions, but they have a nice concave lens and they have high ratings/specs for the phantom power.

http://export.farnell.com/jsp/search/productdetail.jsp?SKU=1736732

Thanks for the encouragement and thoughts everyone!

Mike
 
oops sometimes the links for farnell don't work; just go to farnell.com, find farnell exports link at the bottom, and then put in the sku number it should come up...
 
Glad you found a solution!

I meant to mention that to prevent accidental switching of P48 I use a locking toggle plus the Omron indicator (I like square...) but I use the alternate action buttons for other things

Cheers!

Michael
 

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Phantom? Don't worry about it.

The "open" switch must block the open circuit voltage, 48V. The arcing voltage between round electrodes in air is 300V; even if you get sharp points on the contacts 48V won't jump across.

The closed switch must pass the current. A 100 Ampere contact is a large fraction of an inch. A 10mA contact is 8000 times smaller.... basically the smallest contact which is economic to stamp and assemble will handle 10mA. If it has a handle, it will have big-enough contacts.

Other important considerations:

How many times? If you flip 10 times a second 24/7, you need ample reseve for mechanical wear.

Can there be a "fault"? My house main breaker is rated to break 100A as needed; it is also rated to break 10,000A _once_ without exploding, because a heavy dead-short in the box could suck 10,000A from the street (not MY street, but well-wired homes). In this case your 3K4 Phantom resistors are "permanently" in-line, and limit current to 14mA worst-case, just as the 0.024 ohms of 40 feet of feeder-wire limit house-faults to 10,000A.

If it fails, does anybody die? Big industrial machinery MUST switch correctly. I like my house breaker to be over-rated because if a fire started while I was out the dogs would die. The downside of a failed Phantom is less.

Are we switching nasty loads? Worst-case is large current through a large inductor. When you break, the coil voltage rises toward infinity until the switch breaks-over. On DC supply, ALL the stored energy must be dissipated in this arc. On AC supply there is a tendency for the arc to stop in a half-cycle. (Which is why power tools with AC/DC motors often have AC-only ratings: the switch was not bought to tolerate constant DC breaks.) Switching a large cap onto a voltage is less tough, but is is wise to throw 100 ohms between switch and any 100uFd cap you may have put on the switched side.

> rated for 30VDC

24V-30V falls under different regulations. It is unlikely to electrocute; and for low current it is unlikely to start a fire. (12V 200A car wiring is different and sure can start a fire.) If they claim over 30V, they may have to do many more tests.

Farnell's stupid site shows switches rated to 1mA. That's crazy. Especially for Illuminated switches: the lamp must be taking more than 1mA, and why should the load contacts be weaker?

While I might avoid the 1mA part, any of the 10mA and up will be fine.

> For line level audio signals, chose switches with a lower voltage rating.

Actually, avoid cheap high-power switches. I used 250V 10A toggles to patch coax Ethernet; they were user-rugged. They failed, open. High-power switches use contacts which tarnish. If you switch a 100 watt lamp or 120V 7A motor, the load-power burns off the tarnish faster than it grows. 2 years in a nasty office rarely switching 1V 20mA, they fail. In my network, the whole net was down. In your Phantom, worst is that you have to move to another channel and replace the switch later.
 
Thank-you PRR, I appreciate your time and insights. Basically it sounds like you're saying, "don't worry about it." Well I already ordered the part, so let's hope it holds up.

Thx
 

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